Okay, here's the thing: I have read parts of this manga years ago. I didn't really even like it (in fact, I would go as far as to say I hated it), but it recently came up in conversation with a friend while we were discussing tropes, and for the love of me I cannot remember the title. Here's what I remember about it: The protagonist is your usual average japanese high schooler dude. Then, through some circumstances, he is healed and/or given some blood by a demon girl (or maybe vampire...?), and then he and his little brother are taken to this magical school, where it is shown that he is now weak but has a ton of latent power. Then it turns out that the supernatural world has a rule against taking humans in and giving them power, because they almost always become overpowered tyrants. Then I think the series was axed, so shit happens, the author rushed the ending by having the MC become an item with the demon girl from the beginning, then the little brother is possessed by an ancient evil and disappears. Then there was a sequel series taking place several years later, where the MC is now an evil tyrant, he blamed the demon girl for the disappearance of his brother, so he locked her up in full restraints in a dungeon where he only visits her to drink her blood, and the new protagonist was implied to be their child that she hid away when the old MC went crazy. Does any of that right any bells? I just really want to know and be done with it, as right now this is just like an itch that I just barely can't reach to scratch...